The present invention relates to coffee brewing apparatus in general and more particularly to improvements in apparatus for brewing espresso or capuccino coffee. Still more particularly, the invention relates to improvements in electrically operated espresso coffee brewing apparatus of the type wherein a holder for a sieve or filter containing a supply of powdered coffee beans is detachably connected to a support in or on a housing which contains or carries a supply of fresh water, means for heating the water and means for forcing heated water through the supply of comminuted coffee beans.
Apparatus of the above outlined character are known in a variety of sizes and shapes. They share the feature that the holder for the filter which contains a supply of comminuted coffee beans is detachably secured to the housing, for example, by a bayonet lock or by another suitable quick-release connection. The filter is separably received in the holder so that each of these parts can be independently cleaned as well as that the holder can accept smaller or larger filters.
Many presently known apparatus of the above outlined character exhibit the drawback that the filter is not readily separable from the support for the holder. The situation is aggravated if the holder is not detached from its support immediately or shortly after use. It has been found that the filter exhibits a tendency to adhere to the support, i.e., to become detached from the holder while the latter is being separated from its support. In many instances, the support carries a ring-shaped seal which is engaged by and to which the filter adheres with a force which is sufficiently pronounced to cause separation of the holder from the filter even though the filter should be detached jointly with the holder.
Attempts to prevent adherence of the filter to the support in an espresso coffee brewing apparatus include the provision of means for separably securing the filter to its carrier so that the filter is compelled to share the movements of the carrier with reference to the support. In accordance with one presently known proposal, the securing means comprises a magnet which is mounted at the inner side of the holder and attracts the filter so that the latter becomes separated from the support for the holder in the brewing apparatus. Such securing means exhibit a number of drawbacks. Thus, it is rather difficult to properly install one or more magnets at the inner side of the holder. Secondly, a magnet can attract the filter only if the latter consists at least in part of a ferromagnetic material which contributes to the cost of the filter and reduces the number of materials which can be used for the making of filters. Moreover, the force with which a relatively small magnet attracts the filter is rather small so that the magnet cannot ensure predictable separation of the filter from the support for the holder.